Fixing the Power

I installed my SRM Wireless Friday. The first ride with the wireless unit and Garmin 705 was Saturday's team ride. My power readings seemed to be low for the perceived effort. I thought it was either because I was fatigued (plus it was really hot), or it was because I hadn't mounted the power sensor cube correctly. The weird thing is I was using a dual set up, the wired PCV SRM computer and the wireless Garmin Edge 705. Both were giving me the same readings.
I originally mounted the power sensor over the cable guide, using one washer from a tube. That night I mounted the power sensor under the cable guide. I left the original wired power sensor in it's original place (I have glued on). When I went out for my ride Sunday my power numbers were closer to my RPE. I once again ran the dual set-up of the PCV and Edge. Both computers jived. I thought , cool problem solved. So I removed the wired set-up.
Well today when I was testing things out I wasn't getting any power reading - WTF?! I would occasionally get the Garmin to pick up the power meter, and it would register a slope, but still no cadence or power reading. Then when I reattached the wired power sensor I would get a power reading.
So I removed the wireless power sensor to see if the Garmin would pick-up the power meter; it didn't. So I figured I must have incorrectly mounted the wireless power sensor. This time I mounted it over the cable guide using two tube washers. Viola, it worked. I took my bike for a short test spin and the numbers seemed to match my RPE. Cadence was working, power was working, and I was happy.
The real test will be tomorrow when I do hill repeats. We'll see how my power numbers read while I'm going up Huddart.
So today's lesson is: If you have a Cervelo and you are installing an SRM power meter using a bottom bracket mounted power sensor, you must mount it over the cable guide to get it to read the power correctly. I recommend using two washers from in bike inner tube. You know, the ones that come on the threaded valve stems. Put two of those buggers in between the cable guide and the bottom bracket power sensor mount and run your bolt through and tighten. Problem solved.